Golf ball

ABSTRACT

The present invention provides a golf ball having excellent flyer resistance at a shot on the rough, and having high rebound characteristics and excellent flight performance. The present invention relates to a golf ball comprising a core having a single-layered structure or a multi-layered structure and a cover covering the core, wherein the cover has a complex elastic modulus at −10° C. of 20 to 150 MPa and loss tangent (tan δ) at −10° C. of not less than 0.05, as determined from temperature-dependent curves of the complex elastic modulus and tan δ obtained by dynamic viscoelastic measurement at a frequency of 10 Hz, a dynamic strain of 5% and a heating rate of 4° C./min.

FIELD OF THE INVENTION

[0001] The present invention relates to a golf ball having excellent spin performance. More particularly, it relates to a golf ball having excellent flyer resistance at a shot on the rough, and having high rebound characteristics and excellent flight performance.

BACKGROUND OF THE INVENTION

[0002] Solid golf balls, such as a two-piece golf ball or three-piece golf ball, and thread wound golf balls have been used for round games. The solid golf ball consists of a solid core of integrally molded rubber material comprising polybutadiene as a main component and a cover of thermoplastic resin (e.g. ionomer resin) covering on the solid core. The thread wound golf ball consists of a solid or liquid center, a thread rubber layer formed by winding thread rubber in a stretched state around the center, and a cover of ionomer resin or balata etc. covering on the thread wound layer.

[0003] A golf ball is often placed in a rough or tall lawn by accident in a round play. When one hit the ball from the lawn, a phenomenon called flyer easily occurs, that is, backspin amount is small and ball trajectory is high because of the presence of the lawn between the golf club and the golf ball. The flyer phenomenon would bring about difficulty in controlling the ball trajectory and spin amount and especially causes poor controllability at approach shots, which has been a problem to be solved. The phenomenon occurs regardless of the solid golf ball or thread wound golf ball, and many golf players are troubled with it.

[0004] It has been found in studying the flyer phenomenon with respect to types of covers of golf balls that the flyer occurs more easily on ionomer-cover golf balls than balata-cover golf balls. In case of the golf ball using balata cover, it has been known that the flyer is difficult to occur and the controllability of spin is excellent, but the rebound characteristics of the cover material is poor and the cut resistance is poor. On the other hand, the ionomer resin cover has high elastic modulus and excellent rebound characteristics, but the resulting golf ball having ionomer cover has small spin amount and poor controllability.

[0005] In order to solve the flyer problem and provide a golf ball having excellent rebound characteristics, the present inventors have proposed a selection of a cover material for a golf ball having a complex elastic modulus of 50 to 1500 kgf/cm² (about 5 to 150 MPa) at −10° C. obtained by dynamic viscoelastic measurement and a resilience of not less than 50% obtained by a tripsometer (Japanese Patent Kokai publication No. 305115/1998). However, in the golf ball using the cover material, sufficient flyer resistance has not been obtained, because higher performance has been required for current golf balls for round games.

OBJECTS OF THE INVENTION

[0006] A main object of the present invention is to provide a golf ball having excellent flyer resistance at a shot on the rough, and having high rebound characteristics and excellent flight performance.

[0007] According to the present invention, the object described above has been accomplished by adjusting a complex elastic modulus and tan δ of cover to specified ranges, thereby providing a golf ball having excellent flyer resistance at a shot on the rough, and having high rebound characteristics and excellent flight performance.

SUMMARY OF THE INVENTION

[0008] The present invention relates to a golf ball comprising a core having a single-layered structure or a multi-layered structure and a cover covering the core, wherein the cover has a complex elastic modulus at −10° C. of 20 to 150 MPa and loss tangent (tan δ) at −10° C. of not less than 0.05, as determined from temperature-dependent curves of the complex elastic modulus and tan δ obtained by dynamic viscoelastic measurement at a frequency of 10 Hz, a dynamic strain of 5% and a heating rate of 4° C./min.

[0009] In the cover material which has been proposed by the present inventors as described above (Japanese Patent Kokai publication No. 305115/1998), a complex elastic modulus measured at specified temperature, frequency and dynamic strain is used as a factor showing dynamic hardness, and is adjusted to specified ranges. This technique resides in specifying the dynamic hardness at conditions of approach shots, such as room temperature, high frequency and large deformation amount, and selecting some factors for easily applying spin on balls.

[0010] The present inventors have further studied cover materials in more detail, and have found that there are golf balls which have or have not sufficient flyer resistance in the golf ball using the cover material having such properties as described in our previous invention. This is because the flyer occurs under the specific conditions, which have not considered yet. That is, the behavior of the golf ball when hit in the state of putting the grass between the golf club face and the golf ball is not explained only by the dynamic hardness based on the deformation condition at approach shot. It is required to reconsider how to prevent the flyer from occurring, particularly remarkable properties of the golf ball in the special state described above.

[0011] In the golf ball having excellent flyer resistance, it is required to have sufficient backspin amount when hit in the state of putting the grass between the golf club face and the golf ball. That is, it is difficult to give the golf ball a spin if friction force is not applied between the golf club face and the surface of the golf ball in the state of putting the grass there. The flyer resistance can be improved by maintaining the friction force when hit in the state of putting the grass between the golf club face and the golf ball. Therefore, it is required to remark the properties connected with the friction force.

[0012] Polymer materials used for the cover of golf balls generally have viscoelasticity, that is, have both elasticity and viscosity. The elasticity mainly controls properties such as elastic modulus, flexural strength, hardness and the like of the materials, and the viscosity mainly controls properties such as impact strength, friction force (coefficient of friction) and the like of the materials.

[0013] The present inventors have studied the flyer resistance and properties of the cover materials, and have remarked loss tangent “tan δ”, which represents mechanical damping, in addition to the complex elastic modulus as a factor for representing dynamic hardness. The complex elastic modulus E* and tan δ are represented by the following two formulae:

E*=(E′ ² +E″ ²)½

[0014] tan δ=E″/E′

[0015] (wherein E′ is storage elastic modulus, and E″ is loss elastic modulus.). The δ is an angle, which represents a time lag between stress applied and strain. The loss tangent (tan δ), which is also called coefficient of loss, represents ability of dissipating the stress applied on the material as thermal energy, that is, energy loss. Therefore, when the value of tan δ is large, the value of properties, which depend on viscosity, such as impact strength, friction force and the like is large.

[0016] The friction force F_(f) is generally represented by the following formula:

F _(f) =F _(a) +F _(h) +F _(b)

[0017] (wherein F_(a) is adhesion friction force, F_(h) is hysteresis loss friction force, and F_(b) is abrasion friction force.) Assuming that a bonding strength in a level of molecular rises at the interface between the golf club face and the surface of golf ball, the adhesion friction force is a force that is necessary to shear destruct the bonding strength. The adhesion friction force depends on the contact surface, and is large when the contact area is large.

[0018] The cover on the surface of golf ball repeats compression deformation and recovery behavior along the unevenness of the golf club face contacting with the golf ball at the time of hitting, but energy loss occurs in the cover and is compensated by work from the stress applied from the outer, which work arises hysteresis loss friction force. The hysteresis loss friction force is friction force, which is given by deformation. Abrasion friction force also arises between a golf ball surface and a surface of a golf club, but is not considered for the present invention because no abrasive force applied from the golf ball to the golf club.

[0019] The adhesion friction force has large effect on the golf ball when usually hit in the state of putting no grass between the golf club face and the golf ball. On the other hand, the hysteresis loss friction force has large effect on the golf ball when hit in the state of putting the grass between the golf club face and the golf ball. The lower the hardness, the larger the hysteresis loss friction force. When the hardness is in lower range, the larger the coefficient of loss (tan δ), the larger the hysteresis loss friction force. On the other hand, when the hardness is in higher range, the tan δ is small, and effects therefrom is also small. Therefore it is required to use the cover material, of which the complex elastic modulus representing hardness is small and the tan δ is large in order to improve the flyer resistance.

[0020] In the golf ball of the present invention, it is required for the cover to have a complex elastic modulus at −10° C. of 20 to 150 MPa and loss tangent (tan δ) at −10° C. of not less than 0.05, as determined from temperature-dependent curves of the complex elastic modulus and tan δ obtained by dynamic viscoelastic measurement at a frequency of 10 Hz, a dynamic strain of 5% and a heating rate of 4° C./min. The complex elastic modulus is preferably not more than 100 MPa, more preferably not more than 50 MPa. The tan δ is preferably not less than 0.07. However, when the complex elastic modulus is too small, or the tan δ is too large, the rebound characteristics, which are important factor, are degraded. Therefore the complex elastic modulus is preferably not less than 30 MPa, and the tan δ is preferably not more than 0.3, more preferably not more than 0.11.

[0021] The present inventors have found that the state of having high frequency at room temperature when hitting the golf ball correlates with the complex elastic modulus obtained by dynamic viscoelastic measurement at lower temperature of −10° C. and a frequency of 10 Hz from temperature-frequency conversion law. They have also found that the complex elastic modulus at −10° C. measured at a dynamic strain of 5% correlates with the occurrence of flyer by adjusting the dynamic strain to 5%, which is close to the deformation amount of the golf ball at approach shot (Japanese Patent Kokai publication No. 305115/1998).

DETAILED DESCRIPTION OF THE INVENTION

[0022] In the detailed description of the present invention which follows, the golf ball of the present invention comprises a core and a cover formed on the core. The golf ball of the present invention may be either solid golf ball such as two-piece solid golf ball or thread wound golf ball. The core for solid golf ball (solid core) may be the same one that has been conventionally used, and may be obtained by mixing a rubber composition using a mixer such as a mixing roll, and then vulcanizing (crosslinking) or press-molding the rubber composition in a given mold into a spherical form. The rubber composition comprises 10 to 60 parts by weight of a vulcanizing agent (crosslinking agent), for example, α,β-unsaturated carboxylic acid (such as acrylic acid, methacrylic acid, etc.) or a metal salt thereof, or a functional monomer such as trimethyloipropane trimethacrylate, or a combination thereof; 0.5 to 5 parts by weight of organic peroxides such as dicumyl peroxide, etc.; 10 to 30 parts by weight of filler such as zinc oxide, barium sulfate and the like; optionally antioxidant, based on 100 parts by weight of a base rubber such as polybutadiene. The vulcanization may be conducted, for example, by press molding in a mold at 140 to 170° C. for 10 to 40 minutes.

[0023] The core for thread wound golf ball (thread wound core) comprises a center and a thread rubber layer formed by winding thread rubber in a stretched state around the center, wherein the center may be either liquid center or solid center formed from rubber composition. The thread rubber can be of the same kind which has been conventionally used for the thread rubber layer of the thread wound golf ball. For example, the thread rubber can be obtained by vulcanizing a rubber composition prepared by formulating sulfur, a vulcanization aid, a vulcanization accelerator, an antioxidant and the like to a natural rubber or a blend rubber of the natural rubber and a synthetic polyisoprene. A thread-wound core can be produced by drawing the thread rubber about 1000% and winding it over the center. However, such solid and thread-wound cores are given by way of illustrative examples only, and the invention shall not be limited thereto.

[0024] In the golf ball of the present invention, the core has a diameter of 40.0 to 42.5 mm, preferably 40.3 to 42.0 mm. When the diameter of the core is smaller than 40.0 mm, the volume content of the core is small based on the total volume of the golf ball, and the rebound characteristics are degraded. On the other hand, when the diameter of the core is larger than 42.5 mm, the cover is too thin, and the technical effects of improving the flyer resistance are not sufficiently obtained, or the durability is degraded.

[0025] The cover is then covered on the core. In the golf ball of the present invention, it is required for the cover to have a complex elastic modulus at −10° C. of 20 to 150 MPa and loss tangent (tan δ) at −10° C. of not less than 0.05, as determined from temperature-dependent curves of the complex elastic modulus and tan δ obtained by dynamic viscoelastic measurement at a frequency of 10 Hz, a dynamic strain of 5% and a heating rate of 4° C./min.

[0026] The cover may have a single-layered structure or a multi-layered structure, which has two or more layers. The materials suitably used in the cover of the present invention is not limited as long as the complex elastic modulus and tan δ are within the above ranges, but it is not suitable to use ionomer resin alone, which is general cover material. Particularly, it is effective to use thermoplastic elastomer, ethylene-methacrylic acid copolymer, mixtures thereof with ionomer resin and the like, in order to accomplish high tan δ.

[0027] The thermoplastic elastomer is not limited as long as it is composed of soft segments having rubber elasticity and hard segments (such as a frozen phase or crystalline phase), which restrain plastic deformation, but include polystyrene-based thermoplastic elastomer, polyamide-based thermoplastic elastomer, polyester-based thermoplastic elastomer, polyolefin-based thermoplastic elastomer, polyurethane-based thermoplastic elastomer and the like. The thermoplastic elastomer has only low complex elastic modulus, but can have high tan δ by selecting the soft segments. Preferred are polystyrene-based thermoplastic elastomer. Examples thereof, for example, include SBS resin composed of polystyrene phase (S) and polybutadiene phase (B), SIS resin composed of polystyrene phase (S) and polyisoprene phase (B), SEPS resin composed of polystyrene phase (S) and ethylene/propylene phase (EP), SEBS resin composed of polystyrene phase (S) and ethylene/butylene phase (EB) and the like.

[0028] Examples thereof, which are commercially available, include styrene-based thermoplastic elastomers commercially available from JSR Co., Ltd., under the trade name “TR” series (e.g., “TR2787”) and “SIS” series (e.g., “SIS5000”); styrene-based thermoplastic elastomers commercially available from Asahi Chemical Industry Co., Ltd., under the trade name “Tuftec” series (e.g., Tuftec Z514); styrene-based thermoplastic elastomers commercially available from Kuraray Co., Ltd., under the trade name “Cepton” series (e.g., “Cepton 2002”); styrene-based thermoplastic elastomers commercially available from Aronkasei Co., Ltd., under the trade name “AR” series (e.g., “AR790”); and the like.

[0029] Examples of ethylene-methacrylic acid copolymers, which are commercially available, include ethylene-methacrylic acid copolymers commercially available from Du Pont-Mitsui Polychemicals Co., Ltd., under the trade name “Nucrel” series (e.g., “Nucrel AN4211”, “Nucrel AN4213” and the like).

[0030] The polymer components for cover composition may use as mixtures with the other cover materials having high rebound characteristics, such as ionomer resin, but the thermoplastic elastomer is preferably comprised in amount of not less than 30% by weight in the polymer components for cover composition.

[0031] The ionomer resin may be a copolymer of ethylene and α,β-unsaturated carboxylic acid, of which a portion of carboxylic acid groups is neutralized with metal ion, or a terpolymer of ethylene, α,β-unsaturated carboxylic acid and α,β-unsaturated carboxylic acid ester, of which a portion of carboxylic acid groups is neutralized with metal ion. Examples of the α,β-unsaturated carboxylic acid in the ionomer include acrylic acid, methacrylic acid, fumaric acid, maleic acid, crotonic acid and the like, preferred are acrylic acid and methacrylic acid. Examples of the α,β-unsaturated carboxylic acid ester in the ionomer include methyl ester, ethyl ester, propyl ester, n-butyl ester and isobutyl ester of acrylic acid, methacrylic acid, fumaric acid, maleic acid, crotonic acid and the like. Preferred are acrylic acid esters and methacrylic acid esters. The metal ion which neutralizes a portion of carboxylic acid groups of the copolymer or terpolymer includes a sodium ion, a potassium ion, a lithium ion, a magnesium ion, a calcium ion, a zinc ion, a barium ion, an aluminum, a tin ion, a zirconium ion, cadmium ion, and the like. Preferred are sodium ions, zinc ions, magnesium ions and the like, in view of rebound characteristics, durability and the like.

[0032] The ionomer resin is not limited, but examples thereof will be shown by a trade name thereof. Examples of the ionomer resins, which are commercially available from Du Pont-Mitsui Polychemicals Co., Ltd. include Hi-milan 1555, Hi-milan 1557, Hi-milan 1605, Hi-milan 1652, Hi-milan 1702, Hi-milan 1705, Hi-milan 1706, Hi-milan 1707, Hi-milan 1855, Hi-milan 1856 and the like. Examples of the ionomer resins, which are commercially available from Du Pont Co., include Surlyn 8945, Surlyn 9945, Surlyn 6320, Surlyn AD8511, Surlyn AD8512, Surlyn AD8542 and the like. Examples of the ionomer resins, which are commercially available from Exxon Chemical Co., include Iotek 7010, Iotek 8000 and the like. These ionomer resins may be used alone or in combination.

[0033] The cover composition used in the present invention may optionally contain fillers (such as barium sulfate, etc.), pigments (such as titanium dioxide, etc.) and the other additives such as a dispersant, a plasticizer, an antioxidant, a UV absorber, a photostabilizer and a fluorescent agent or a fluorescent brightener, etc., in addition to the polymer component as a main component as long as the addition of the additives does not deteriorate the desired performance of the golf ball cover.

[0034] It is desired for the cover of the golf ball of the present invention to have a thickness of 0.3 to 3.5 mm, preferably 0.8 to 2.5 mm. When the thickness is smaller than 0.3 mm, the technical effects of improving the flyer resistance are not sufficiently obtained, or the strength is low, and the durability is degraded. On the other hand, when the thickness is larger than 3.5 mm, the volume content of the core is small based on the total volume of the golf ball, and the rebound characteristics are degraded.

[0035] A method of covering on the core with the cover is not specifically limited, but may be a conventional method. For example, there can be used a method comprising molding the cover composition into a semi-spherical half-shell in advance, covering the core with the two half-shells, followed by press molding at 130 to 170° C. for 1 to 5 minutes, or a method comprising injection molding the cover composition directly on the core, which is covered with the cover, to cover it.

[0036] In the injection molding, when the thermoplastic elastomer is used, it is injected with flowable state by heating, followed by cooling, and then pulled out with solidified state. On the step of molding the cover composition into a semi-spherical half-shell in press molding, when the thermoplastic elastomer is used, it is injected with flowable state by heating, followed by cooling, and then pulled out with solidified state as described in the injection molding.

[0037] At the time of molding the cover, many depressions called “dimples” may be optionally formed on the surface of the golf ball. Furthermore, paint finishing or marking with a stamp may be optionally provided after the cover molded for commercial purposes. Factors, which have an effect on the shape and surface of the cover, have an effect on the friction force and spin of the golf ball when the golf ball directly contacts with the golf club face, but have no effect on the flyer resistance when putting the grass between the golf club face and the golf ball. The golf ball of the present invention is formed, so that it has a diameter of not less than 42.67 mm (preferably 42.70 to 43.20 mm) and a weight of not more than 45.93 g, in accordance with the regulations for golf balls.

[0038] In the golf ball of the present invention after covering with the cover, it is desired to have a compression (a deformation amount, when applying from an initial load of 98 N to a final load of 1275 N) of 2.2 to 4.5 mm, preferably 2.5 to 3.3 mm, more preferably 2.9 to 3.2 mm. When the deformation amount is smaller than 2.2 mm, the golf ball is too hard, and the shot feel is poor. On the other hand, when the deformation amount is larger than 4.5 mm, the golf ball is too soft, and the rebound characteristics are degraded, which reduces the flight distance.

EXAMPLES

[0039] The following Examples and Comparative Examples further illustrate the present invention in detail but are not to be construed to limit the scope of the present invention.

Production of Core

[0040] The rubber composition for the core having the formulation shown in Table 1 was mixed, and then vulcanized by press-molding at 155° C. for 18 minutes in the mold to obtain spherical solid core having a diameter of 38.5 mm. TABLE 1 Core Amount composition (parts by weight) Polybutadiene*1 100 Zinc acrylate 33 Zinc oxide 9.7 Barium sulfate 9.7 Dicumyl peroxide 1.0 Antioxidant*2 0.2

Preparation of Cover Compositions

[0041] The formulation materials showed in Table 2 were mixed at 160 to 180° C. using a kneading type twin-screw extruder to obtain pelletized cover compositions. The extrusion condition was,

[0042] a screw diameter of 45 mm,

[0043] a screw speed of 200 rpm,

[0044] a screw L/D of 35, and

[0045] a cylinder temperature of 210° C.

[0046] With respect to the resulting cover composition, a complex elastic modulus and tan δ at −10° C. was determined by dynamic viscoelastic measurement. The result is shown in Tables 3 and 4. TABLE (parts by weight) Ex- Cover ample com- No. Comparative Example No. position 1 2 1 2 3 4 5 6 7 AR790*3 70 — 100 — — — — — — Nucrel — 50 — 100 — — — — — AN4213*4 Nucrel — — — — 100 — — — — AN4311*5 Hytrel — — — — — 100 — — — 4047*6 Elastollan — — — — — — 100 — — ET850*7 Hi-milan 30 50 — — — — — 100 — 1706*8 Cepton — — — — — — — — 100 2002*9 # available from Aronkasei Co., Ltd. # from Du Pont-Mitsui Polychemicals Co., Ltd. # from Du Pont-Mitsui Polychemicals Co., Ltd. # from Toray-Du Pont Co., Ltd. # available from Takeda Badische Urethane Industries, Ltd. # by neutralizing with sodium ion, manufactured by Du Pont-Mitsui Polychemicals Co., Ltd. # available from Kuraray Co., Ltd.

Examples 1 to 2 and Comparative Examples 1 to 7

[0047] The cover compositions were covered on the core obtained as described above by injection molding. Then, deflashing, surface pretreatment for painting, paint and the like, which are generally done on the surface of a golf ball, were conducted on the surface to produce a two-piece solid golf ball having a diameter of 42.7 mm. With respect to the resulting golf balls, the flight distance, compression (deformation amount) and flyer resistance were measured or evaluated. The results are shown in Tables 3 and 4. The test methods are as follows.

[0048] (Test method)

[0049] (1) Dynamic viscoelastic measurement

[0050] A specimen of 4 mm (width)×30 mm (length)=0.5 mm (thickness) prepared from the cover composition is forcibly vibrated using a viscoelastic spectrometer DVA 200 type, manufactured by Shimadzu Co. at the following conditions, to measure a vibration amplitude ratio and a phase lag between drive part and response part, whereby temperature-dependent curves of a complex elastic modulus and tan δ were obtained.

[0051] Deformation mode: simple stretching (in the direction of the length)

[0052] Frequency: 10 Hz

[0053] Dynamic strain: 5% (0.2 mm)

[0054] Measuring temperature range: −50 to 50° C.

[0055] Heating rate: 4° C./min

[0056] The values of the complex elastic modulus at −10° C. and tan δ at −10° C. determined from the temperature-dependent curves are shown as the complex elastic modulus and tan δ of each cover.

[0057] (2) Flight performance

[0058] A No. 1 wood club (W#1, a driver) was mounted to a swing robot manufactured by True Temper Co. and the resulting golf ball was hit at a head speed of 45 m/sec, the flight distance was measured. As the flight distance, carry that is a distance to the dropping point of the hit golf ball was measured. The measurement was conducted by using 8 golf balls for every sample (n=8), and the average is shown as the result of the golf ball.

[0059] (3) Ball compression

[0060] The ball compression is determined by measuring a deformation amount, when applying from an initial load of 98 N to a final load of 1275 N on the golf ball.

[0061] (4) Flyer resistance

[0062] At approach shot using a pitching wedge, the spin amount (P₁) when commonly hit in the state of teeing up, and the spin amount (P₂) when hit from a rough 4 cm in depth were measured, and the flyer resistance was determined by calculating the ratio (P₂/P₁=100). When the value is smaller, the golf ball is easier to occur the flyer. On the other hand, when the value is larger, the golf ball is more difficult to occur. The measurement was conducted by 10 high-level golfers according to practical hitting test, and the average is shown as the result of the golf ball.

[0063] (Test results) TABLE 3 Comparative Example No. Example No. Test item 1 2 1 2 3 (Cover) Complex elastic 29.4 49.0 9.8 14.7 2.9 modulus (MPa) Tan δ 0.07 0.11 0.12 0.18 0.22 (Golf ball) Flight distance (m) 204 206 200 201 191 Compression (mm) 3.14 2.96 3.55 3.31 3.70 Flyer resistance 66 64 67 67 68

[0064] TABLE 4 Comparative Example No. Test item 4 5 6 7 (Cover) Complex elastic 49.0 9.8 14.7 2.9 modulus (MPa) Tan δ 0.11 0.12 0.18 0.22 (Golf ball) Flight distance (m) 199 190 207 201 Compression (mm) 3.64 3.78 2.85 3.26 Flyer resistance 30 65 32 66

[0065] As is apparent from the results of Tables 3 to 4, the golf balls of the present invention of Examples 1 to 2, which adjust the complex elastic modulus and tan δ of the cover to specified ranges, have excellent flyer resistance and long flight distance, when compared with the golf balls of Comparative Examples 1 to 7.

[0066] On the other hand, in the golf balls of Comparative Examples 1 to 3 and 7, the flyer resistance is excellent because the cover has large tan δ, but the complex elastic modulus of the cover is small, and the flight distance is short. In the golf ball of Comparative Example 4, the complex elastic modulus of the cover is small, and the flight distance is short. In addition, the tan δ is small, and the flyer resistance is poor.

[0067] In the golf ball of Comparative Example 5, the flyer resistance is excellent because the tan δ of the cover is large, but the complex elastic modulus of the cover is small, and the flight distance is short. In the golf ball of Comparative Examples 6, the flight distance is long because the complex elastic modulus of the cover is large, but the tan δ of the cover is small, and the flyer resistance is poor. 

What is claimed is:
 1. A golf ball comprising a core having a single-layered structure or a multi-layered structure and a cover covering the core, wherein the cover has a complex elastic modulus at −10° C. of 20 to 150 MPa and a loss tangent (tan δ) at −10° C. of not less than 0.05, as determined from temperature-dependent curves of the complex elastic modulus and tan δ obtained by dynamic viscoelastic measurement at a frequency of 10 Hz, a dynamic strain of 5% and a heating rate of 4° C./min.
 2. The golf ball according to claim 1, wherein the cover comprises 30% by weight of thermoplastic elastomer in a base polymer.
 3. The golf ball according to claim 1 or 2, wherein the cover is formed from materials selected from the group consisting of thermoplastic elastomer, ethylene-methacrylic acid copolymer and mixtures thereof with ionomer resin. 